Pulse-modulated wave-signal receiver



D. B. HOISI'NGTON Filed Aug. 15, 1944 PULSE-MODULATED WAVE-SIGNAL RECEIVER mmiwasa 0 Nov. 5, 1946.

Nov. 5, 1946. D. B. HOISINGTON PULSE-MODULATED WAVE-SIGNAL RECEIVER Filed Aug. 15, 1944 3 Sheets-Sheet 2 l-l A My T m; mm 0 E H ma m Y A DB A RNEY Nov. 5, 1946.

D. B. HOISI NGT'ON PULSE-MODULATED WAVE-SIGNAL RECEIVER- s sheets-sheet 3 Filed Aug. 15, 1944 Patented Nov. 5, 1946 PULSE-MODULATED WAVE-SIGNAI 4 RECEIVER David B. Hoisington, Little Neck, N. Y., assignor, by'mesne assignments, to Hazeltine Research, Inc., Chicago, 111., a corporation of Illinois Application August 15, 1944, Serial No. 549,616

13 Claims. (c1. 250-20) This invention relates, in general, to a receiver for deriving desired modulation components of a received pulse-modulated carrier-frequency wave signal. It is particularly directedto such a receiver which is subject to receive an interfering continuouswave signal concurrently with and having a different carrier frequency than the desired pulse-modulated signal. While the invention is subject to a variety of applications, it is especially suited for inclusion in the receiver portion of a radio-locator or direction-finder system and will be described in that connection.

Direction-finder systems of the prior art having a receiver of the superheterodyne type and the effects thereon of an interfering continuouswave signal will first be considered. It is to be noted at the outset that such a system is usually operated in the ultra-high portion of the frequency spectrum because of the present allocation of available radio-frequency channels and also to take advantage of improved directivity possible at ultra-high frequencies. Since allowance must be made for drifts in the operating frequency of the heterodyne oscillator and in the carrier frequency of the transmitted signal, at least the initial stages of such receivers are required to have a wide pass band to assure reception of the desired direction-finder signals. At the same time, this band-width characteristic renders the receiver subject to interfering signals of a correspondingly wide range. When the interfering signal has a high intensity, compared with that of a desired pulse-modulated direction-finder signal, it causes overloading or blocking in many of the prior art receivers to such an extent that the pulse-modulated signal is not translated. In other words, the desired direction-finder signal is lost under the stated condition. Obviously, this is an undesired limitation.

In certain other'prior art receivers of the type under consideration the band width is materially reduced in stages following the second detector. The change in band width is desired to increase the signal-to-noise ratio of the receiver but impedes efficient operation in the presence of strong interference. Usually the band width of the stages following the second detector of such a receiver is selected to be only as wide as required to translate the desired modulation components of a received pulse-modulated direction-finder signal. Assume astrong interfering continuous-Wave signal to be received concurrently with the pulse-modulated signal and .also assume the design of the receiver to be such that both received signals are faithfully translated to the second detector. For this condition the aforementioned prior art receiver produces a heterodyne-component pulse-modulated signal in the'output circuit of the second detector, con-- taining the desired modulation components and having a carrier frequency equal to the diflerence between the carrier frequencies of the received pulse-modulated and continuous-wave signals. For the most part, at the operating frequencies of such a system, the carrier frequency of this heterodyne-component signal falls outside of the narrow pass band of the succeeding receiver stages and thus is effectively lost, even though this heterodyne-component signal includes a major portion of the energy content of the translated signals corresponding to the modulation components desired. Further, such prior art arrangements do not include means for deriving the desired modulation components of the heterodyne-component signal should its carrier frequency be such as to be translated by the narrow-band stages succeeding the second detector. It will be appreciated that this operating limitation may likewise be undesirable in many installations.

It is, therefore, an object of the invention to provide an improved receiver for deriving desired modulation components of a received pulsemodulated carrier-frequency wave signal and which avoids one or more of the above-mentioned limitations of prior art arrangements.

It is another object of the invention to provide an improved receiver for deriving desired modulation components of a received pulse-modulated carrier-frequency wave signal even in the presence of a strong interfering wave signal received concurrently therewith and having a carrier frequency different than that of the pulse-modulated signal.

In accordance with the invention, a receiver for deriving desired modulation components of a received pulse-modulated carrier-frequency wave signal but subject to receive concurrently therewith an interfering wave signal of different frequency than the carrier frequency of the pulsemodulated signal comprises a first signal-translating means including selector circuits for translating both of the received signals. The first signal-translating means also includes detecting means effective in the absence of the interfering wave signal to derive the desired modulation components of the pulse-modulated signal and effective in the presence of the interfering signal with high intensity to derive from the received signals of a heterodyne-component pulse-modulated signal having modulation components corresponding to the desired components. The receiver is provided with a second signaltranslating means coupled to the afore-mentioned detecting means and including selector circuits for translating both the desired modulation components and the heterodyne-component pulse-modulated signal. A rectifying means is included in the second signal-translating means eflectlve to derive the desired modulation components from the heterodyne-componeht pulse-modulated signal. Additionally, the receiver is provided with means, coupled to the second signal-translating means, for supplying the desired modulation components to a utilizing device.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Referring to the drawings, Fig. 1 is a schematic representation of a pulse-modulated signal receiver in accordance with the invention; Figs. 2, 3 and 4 individually comprise a series of graphs utilized in explaining the operation of the Fig. 1 arrangement under several different operating conditions; and Fig. 5 is a schematic representation of a modified pulse-modulated signal receiver embodying the invention.

Referring now more particularly to Fig. 1 of the drawings, the arrangement there represented may be considered as constituting the receiver portion of a direction-finder system in which direction-finding information is translated by way of pulse-modulated carrier-frequency wave signals. Accordingly, the receiver is adapted to derive desired modulation components of a received pulse-modulated carrier-frequency wave signal for application to a utilizing device but is also subject to receive concurrently therewith an interfering wave signal of different frequency than the carrier frequency of the received pulsemodulated signal. As illustrated, the receiver comprises an antenna system I0, I l for intercepting pulse-modulated carrier-frequency wave signals and for applying such signals to a first signal-translating means coupled to the antenna 50 system.

The first signal-translating means comprises a radio-frequency amplifier I2 of one or more stages to which are coupled, in cascade, an oscillator-modulator l3, an intermediate-frequency amplifier l4, described more particularly hereinafter, and a detecting means i6. Units l2 and I3, shown in block form, may be of any conventional construction and design. The heterodyning oscillator of unit it in the usual case will have a tendency to drift, that is, its operating frequency will tend to vary over a predetermined range of frequencies. Therefore, units l2 and i3 are preferably selected to have a correspondingly wide band-pass characteristic so as to allow for such instability or frequency shifts of the heterodyning oscillator as well as shifts of the carrier frequency of signals to be received.

The intermediate-frequency amplifier i4 is shown as a three-stage amplifier, although as many stages of amplification may be utilized as desired. In the illustrated arrangement. the stages include pentode-type amplifying tubes 20, 2i and 22. The first stage is coupled to oscillator-modulator it through a coupling condenser 28 and a series-tuned circuit provided by an adiustable inductor 2t and a condenser 25, the tuned circuit being coupled to the input electrodes of tube 20 by way of a resistor 26. An operating bias for tube 20 is supplied by a cathode-- biasing resistor 21. A parallel-tuned circuit is coupled to the anode electrode of'tube 20 and includes an adjustable inductor 28 which is tuned by a condenser 29, shown in broken-line construction since it may be comprised in whole or in part of the inherent capacitance of inductor 28 and associated stray capacitances. Tuned circuit 28, 28 is damped by a resistor 30.

The second intermediate-frequency amplifier stage is coupled to the output circuit of tube 20 through a coupling condenser 3|. This stage is similar to the preceding one, having a damped tuned circuit coupled to the output circuit of its amplifying tube ii. The tuned circuit consists of an adjustable inductor 32, a condenser 33, and a resistor 34. A positive potential is applied to the input electrode of tube 2| through a bleeder network including resistors and 36 coupled to a voltage source, indicated +3. The cathodebias resistor 31 of this stage has a high value, for a purpose to be described hereinafter. The final stage of the intermediate-frequency am,- plifier, including tube 22, is substantially the same as the second stage and corresponding components are identified by like reference numerals primed.

Suitable operating potentials are applied to the several stages from the source indicated +B. A variable resistor 38 is included as a common element in the anode-cathode circuits of. the amplifying stages of unit M to adjust the cathode bias of the several tubes. thereby to provide a gain control. Additional gain control is aiforded by an adjustable resistor 89 coupled between 40 source +3 and the cathode electrodes of tubes 5 cuits. The circuits are stagger-tuned in conventional manner and the damping provided is such that the circuits have a band-pass characteristic substantially as wide as that of units l2 and ii. That is, the selector circuits permit the received signals to be translated faithfully through the intermediate-frequency stages.

The detector ii of the described signal-translating means comprises means effective in the absence of an interfering wave signal to derive desired modulation components of a received pulse-modulated wave signal and effective in the presence of an interfering wave signal of high intensity to derive from the received signals a heterodyne-component pulse-modulated signal 80 having modulation components corresponding to substantially as wide as that of the first signaltranslating means for translating both the desired modulation components and the heter- 5 odyne-component pulse-modulated signal derived in the load circuit of detector l5 under various operating conditions. The second signal-translating means includes an amplifier 50 having a pair of cathode-coupled amplifying tubes 5| and 52. The output signal of detector a T-type network including resistors 55, 56 and 51. With this circuit arrangement, tube 52 constitutes a cathode-driven amplifier. A source of space current, indicated +B, is connected with the anode electrodes of tubes 5| and'52, as shown, and a positive potential is applied t the control electrodes thereof through a bleeder network of resistors 58, 59 and 60. The components of the described T network are selected of such value that tubes 5| and 52 have the desired effective operating bias.

A limiter 65 is coupled in cascade with tube 52 through a condenser 66. The limiter 55 is similar to unit 5|) in that it contains a pair of cathodecoupled electron-discharge repeater devices, illustrated as individual sections of a duo-triode 61 having a common cathode resistor 68. The anode electrodes of each section of tube 61 connect with" a source of space current +3 and a positive potential is applied to the control electrodes of each section through a network of resistors 69, I and II, The resistor elements 68-", inclusive, are proportioned to establish such operating biases on the control electrodes of the sections of tubes 61 that the first section 61A eifects limiting of strong applied signal variations of negative polarity, while limiting of strong signal variations of positive polarity is accomplshed in the remaning section 613. This limiting action in each instance is obtained by the sections being driven to anode current cutoff by the signal variations limited in the particular section.

The second signal-translating means also includes a rectifying means 15 which effectively comprises a full-wave rectifier for deriving the desired modulation components from the heterodyne-co-mponent pulse-modulated signal obtained from detector |5 in the presence of a received pulse-modulated signal and a strong interfering continuous-wave signal of different frequency than the carrier frequency of the pulsemodulated signal. This rectifying means is substantially the same as the signal-translating system forming the subject matter of applicants copending application, Serial No. 549,615, filed concurrently herewith and assigned to the same assignee as the present invention.

The arrangement of unit 15 is described in the copending application as a signal-translating system for translating 3, signal which may include bidirectional amplitude variations with respect to a reference amplitude level. Briefly, the system comprises a first repeater device including section 16A of a duo-triode 16. This section is biased substantially to anode current cutoff by virtue of a stabilizing circuit including a diode 11, so that it is responsive substantially only to amplitude variations of an applied signal in a.

given direction from its reference level. That is,

repeated device 16A is effective to repeat only signal variations of positive polarity. The system also includes a second repeater device, section 5 16B of tube I6, biased so as to be responsive to bidirectional amplitude variations, or variations of positiv and negative polarity, of the applied signal from its reference level. Input and output circuits are provided for the repeater devices, in cluding an impedance which is common to the output circuit of the first device and to the input circuit of the second device. This impedance is shown as series-connected cathode resistors 18 and 19 and is such that signal variations in the first device 16A tend to effect opposing signal variations in the second device 16B. The system has means, comprising a coupling condenser 80, for applying the signal output. of limiter section 613 with a given phase and given intensity to the input circuit of first device 16A. The system likewise has means, comprising a coupling condenser 8| connected to a tap on the anode resistor l2 of limiter section 613, for applying the signal output of section 613 with the same phase but with substantially less than the aforesaid given intensity tothe input circuit of second device '|6B. Preferably, the tap of resistor 12 is so adjusted that the signal is applied to repeater device 163 with less than one-half the intensity of the signal as applied to repeater device 61A. Finally, the system includes means, comprising a connection 82, coupled to the output circuit of the second repeater device for deriving an output signal from the system having amplitude variations which are determined by the variations of the applied signal but which are unidirectional with respect to a reference amplitude level corresponding to the reference level of the applied signal. A detailed description of unit 15 is contained in the above-mentioned copending application.

The receiver of Fig. 1 further includes means coupled to the signal-translating means comprising units 50, 65 and 15 for supplying the desired modulation components to a utilizing device. This means is provided by a cathode follower including a pentode-type tube 90. The cathode follower is coupled to the output circuit of second repeater device 163 through connection 82 and 50 a coupling condenser 9|. A source of space current, indicated +B, is connected with anode electrode of tube 90. The desired modulation components of the received pulse-modulated signal are derived across a cathode impedance 92 and 55 supplied to an output terminal 93 to which a suitable utilizing device (not shown) may be connected. The anode resistor 83 of repeater 16B and the inherent capacitance of its anode circuit, represented by broken-line condenser 84, effectively 60 constitute a low-pass filter in the input circuit of cathode follower 90 so that substantially only the desired modulation components are translated therethrough to output terminal 93. In other words, while the selector circuits of the several operation for the condition in which the desired pulse-modulated direction-finder signal alone is intercepted by antenna system 10, H. A single pulse of the received signal is represented by curve a. The received signal is translated through units I! to IE, inclusive, in accordance with conventional heterodyne operation, and the detected modulation components thereof appear in the output circuit of detector IS with the wave form of curve b. The derived output signal, after amplification in unit 50, is translated through limiter 65 where the first section 61A limits the signal at-the limitinglevel represented by horizontal line c of Fig. 2. The output signal of the limiter, full-line curve d, is a unidirectional signal having only amplitude variations of negative polarity from a reference amplitude level, indicated e1. This output signal of limiter 65 is applied through condenser 80 to the input circuit of first repeater device "A of unit Ill with a given phase and full intensity. The same signal is applied with the like phase but with less than half intensity through condenser 8| to the input circuit of second repeater device "B. The applied signal, having only amplitude variations of negative polarity,'is not translated by first repeater device "A. However, the second repeater, functioning in a manner analogous to a conventional triode amplifier, translates the signal of less than half intensity to the output circuit of detector 15 where it appears with the wave form of curve It. This signal has unidirectional amplitude variations determined by the amplitude variations of the applied signal, curve d, but of positive polarity with respect to a reference amplitude level as corresponding to the reference level er of the applied signal. The desired modulation components of this output signal of unit 15 are selected in the input circuit of cathode follower so and supplied to output terminal 53 for utilization. By stating that the reference level e: of the output signal of unit 15 corresponds to the reference level er of the signal applied thereto is meant that the amplitude level of the output signal has the value e: when the applied signal has its reference amplitude value e1.

From the foregoing description it will be apparent that when the pulse-modulated signal alone is received, the arrangement of Fig. 1 functions as a conventional superheterodyne receiver, deriving the desired modulation components in the second detector l5 and translating these components after suitable amplification in the succeeding signal stages 50, 65 and 1'5 to output terminal 93.

Consider now the operation of the receiver when an interfering continuous-wave signal of relatively low intensity is received concurrently with the pulse-modulated direction-finder signal. The response of the receiver for this condition is represented by the graphs of Fig. 3. The curve a represents the pulse-modulated signal and curve I represents an interfering continuous-wave signal having a carrier frequency different from that of the pulse-modulated signal but included within the pass band of units lll, inclusive. For this condition, both signals are translated to detector II in view of the wide band-pass characteristics of the preceding stages. The output signal of the detector, as shown by curve 12', contains a low-intensity direct current component, the detected modulation components of the received pulse-modulated signal and a superposed ripple component g. The ripple component represents a heterodyne-component signal resulting a r s from intermodulation of the pulse-modulated and interfering signals. It has a frequency corresponding to the diflerence in the carrier frequencies of these received signals but has a relatively low intensity compared with the detected pulse-modulated signal. The ripple component is effectively removed through the limiting action of section "A of unit 65 so that the signal applied to unit 15, as represented by curve d', is

substantially the same as that obtained in the presence of the pulse-modulated signal alone.

Consequently, the output signal of detector ll, curve It, and that delivered to terminal ll correspond to thoseobtained for the first-mentioned operating condition.

Beforeconsidering the over-all response of the receiver to a pulse-modulated signal and a strong interfering continuous-wave signal received concurrently therewith, mention should be made of the function of the biasing circuits of the second and third intermediate-frequency amplifier stages described above. While a positive potential is applied to the control electrodes of tubes 2| and 22, the cathode resistors 31 and 31' of these stages are selected of such value that the eflective grid bias operates the tubes close to anode current cutofi. Due to the curvature of the characteristic curves of tubes II and 22 at the selected operating point, any signal voltage on the input electrodes tends to increase the average space current since positive half cycles of the applied signal increase the space current more than negative half cycles decrease it. Due to the positive voltage on the control electrodes and due to the large cathode resistors, a small change in the space current produces a relatively large change in the operating bias. High-intensity continuous-wave signals move the operating point beyond anode current cutofl so that such high-intensity signals may be accommodated without overloading the intermediate-frequency stages on the positivesignal peaks. For this reason, high-intensity interfering signals do not produce such over-loading as would cause the 45 desired pulse-modulated signal received concurrently therewith to be eflectively lost.

The graphs of Fig. 4 indicate the over-all receiver response when the interfering continuous-wave signal is of high intensity as compared 50 with that of the pulse-modulated signal. These graphs correspond with those of Fig. 3 and are identified by similar reference characters double primed.

It will be seen that for such operating condi- 55 tions, the output signal of the detector l5, curve 1)", comprises a substantial direct current component and a heterodyne-component pulse-modulated signal having modulation components corresponding to the desired components of the re- 60 ceived pulse-modulation signal and having a carrier-frequency equal to the difierence between the carrier frequencies of the received signals.

In other words, the detected modulation components derived directly through detection of the received pulse-modulated signal are overwhelmed by the heterodyne-component signal resulting from the intermodulation of the received pulsemodulated and continuous-wave signals. Since capacitive coupling is utilized between the second 70 detector I5 and amplifier 50, the direct current component of the detector output signal is lost and the signal of curve b is applied to unit 50 as a pure alternating current signal. Both the positive and negative amplitude variations of this 76 signal are limited in unit 65, as indicated by limiting levels and c' of Fig. 4. The resulting signal output of the limiter is represented by full-line curve d". It has bidirectional amplitude variations from a reference level e1" corresponding to the alternating current axis of the heterodynecomponent pulse-modulated signal. The limited signal is translated by detector 16, appearing in the output circuit thereof with the wave form of curve h". The translated signal has amplitude variations which are determined by the bidirectional amplitude variations of the limited signal of curve d" but which are unidirectional with respect to a reference amplitude level ea" corresponding to the reference level er" of the limited signal. From a comparison of curves (1" and h" it will be evident that the unit I functions as a full-wave rectifier. The specific operation of unit 15 in this respect is completely described in the above-mentioned copending application.

While the output signal of curve h" includes the desired modulation components of the received pulse-modulated signal, it also contains a component having twice the frequency of the heterodyne-component pulse-modulated signal obtained from detector I5. This high-frequency component. as well as others not desired to be utilized, are effectively eliminated by the filter 83, 84 in the input circuit of cathode follower 90. Therefore, the signal delivered to output terminal 93 for application to the utilizing device again contains substantially only the desired modulation components of the received pulse-modulated direction-finder signal. g

In order to simplify the description, the response of the receiver has been considered only for the condition in which a given interfering signal of high intensity is received concurrently with the desired pulse-modulated signal. However, it will be clear that an interfering signal having a carrier frequency within a range of frequencies corresponding to the pass band of the receiver may be translated simultaneously with a desired pulse-modulated signal. For this reason, the resulting heterodyne-component pulsemodulated signal derived in detector I5 may likewise have a carrier component within a corresponding frequency range. I Since the pass band of the second signal-translating means comprised of units 50, 65 and I5 is as wide as that of the preceding stages, any such heterodyneecomponent signal is translated thereby to derive the desired modulation components in the described manner.

In one embodiment of the invention found to have practical utility, the receiver had the following characteristics:

Pass band of units IZ-I 5, inclusive megacycles 4 Pass band of units 50, 65 and I5 do 4 Pass band of cathode follower 90 kilocycles 200 Mid-frequency of radio-frequency stages megacycles 172 Mid-intermediate frequency do 11 Pulse-repetition frequency cycles 400 The receiver arrangement of Fig. 5 is generally similar to that of Fig. 1 and corresponding components thereof are identified by the same reference numerals, with exceptions as noted hereinafter. In the Fig. 5 modification the second signal-translating means coupled to detector I5 effectively comprises a pair of parallel-connected signal-translating channels. One such channel comprises a narrow-band amplifier I00 which may be of conventional construction. This channel is characterized by a band-pass characteristic such as to translate substantially only the desired modulation components of the received pulse-modulated direction-finder signal. The other channel is generally similar to the described second signal-translating means of the Fig. l arrangement, having a relatively wide band-pass characteristic. In particular, this channel comprises a unit 50 which here designates both the wide-band amplifier 50 and limiter 05 of the Fig. 1 arrangement. This channel also includes the full-wave rectifier I5 and its'band-pass characteristic is such that the channel is effective to translate any heterodyne-component pulsemodulated signal derived in detector I5 in the presence of both a pulse-modulated signal and a strong interfering continuous-wave signal, as described above. Preferably, the pass band of this second channel comprising units 50 and I5 is such as to translate substantially only such heterodyne-component pulse-modulated signals of detector I5. The desired modulation components derived from the heterodyne-component signal in rectifier I5 are supplied to the narrowband amplifier which may comprise a cathode follower arranged to translate substantially only the desired modulation components, as in the Fig. 1 arrangement.

The modified receiver also includes means coupled to the described pair of parallel-connected channels for supplying the desired modulation components to the utilizing device. This means is provided by an output terminal 93 to which the first channel is coupled through a condenser IOI, while the second channel is coupled thereto through amplifier 90 and a condenser 92.

In general, the two channels coupled to detector I5 will not be used simultaneously and, therefore, the arrangement is Provided with an amplitude-selective means responsive to an interfering wave signal of high intensity for disabling the first-described channel. This means, as represented, includes a relay I02 of well-known construction connected in the output circuit of detector l5. An armature I05 normally connects the first channel, including narrow-band amplifier I00, to the output circuit of detector I5 through a condenser I04 and normally closed contact I03. In its alternate position the armature disables the first channel and connects the second channel to the output circuit of detector l5 through condenser 53 and the remaining relay contact I 06.

The operation of the Fig. 5 arrangement will be apparent from the preceding discussion. Briefly, when a pulse-modulated direction-finder signal alone is received, the desired modulation components are derived indetector.I5 and applied through normally closed contact I03 and narrow-band amplifier I00 to output terminal 93. However, when a strong interfering continuous-wave signal is simultaneously received, the average current in the output circuit of detector I5 has such value that relay I02 is energized and connects the output circuit of the detector with the alternate parallel-connected signal-translating channel. For this condition, the desired modulation components are derived in full-wave rectifier I5 and applied through narcomponents require an unusually wide band-pass characteristic if the signal is to be translated with no distortion. Such fidelity, however, is seldom required and in the usual installation only a selected portion of those components are utilized in the receiver. The expression desired modulation components," as used throughout this specification, is intended to include such a selection of the frequency components of a received pulse-modulated signal.

While the invention has been particularly described in connection with a receiver of the superheterodyne type, it will be understood that this is not a necessary limitation, It will" be obvious to those skilled in the art that the invention may likewise be applied to other receivers,- for example, the tuned radio-frequency type.

In discussing the receiver response in the presence of an interfering continuous-wave signal of high intensity with reference to, and of a carrier frequency different than, the received pulsemodulated signal, it was shown that a heterodyne-component pulse-modulated signal is produced which includes the desired modulation components. This same general operation prevails whether the interfering signal is a continuouswave signal in a strict sense of the term or is a keyed continuous-wave signal having a long duty cycle with reference to the pulse duration of the received direction-finder signal. Also, substantially the same result is obtained when the continuous-wave signal has a sinusoidal or other modulation at a frequency which is low with reference to the period of the received pulses.

The rectifier l5, utilized in deriving the desired modulation components from the heterodyne-component pulse-modulated signal, is disclosed as a full-wave rectifier. This represents the preferred embodiment of the invention, increasing the energy level of the desired modula-' tion components to a value comparable to that obtained when the pulse-modulated signal is received with no interference. It will be unders 'ood that a half-wave rectifier may be employed. if desired.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A receiver for deriving desired modulation components of a received pulse-modulated carrier-frequency wave signal but subiect to receive concurrently therewith an interfering wave signal of diiferent frequency than the carrier frequency of said pulse-modulated signal comprising, a first signal-translating means including selector circuits for translating both of said received signals, detecting means included in said first signal-translating means effective in the absence of said interfering wave signal to derive said desired modulation components of said pulsemodulated signal and effective in the presence of said interfering signal with high intensity to derive from said received signals a heterodynecomponent pulse-modulated signal having modulation components corresponding to said desired components, a second signal-translating means coupled to said detecting means and including selector circuits for translating said desired modulation components and said heterodyne-component pulse-modulated signal, rectifying means included in said second signal-translating means eifective to derive said desired modulation components from said heterodyne-component pulsemodulated signal, and means coupled to said second signal-translating means for supplying said desired modulation components to a utilizing device.

2. A receiver for deriving desired modulation components of a received pulse-modulated carrier-frequency wave signal but subject to receive concurrently therewith an interfering wave signal of different frequency than the carrier frequency of said pulse-modulated signal comprising, a first signal-translating means including selector circuits for translating both of said received signals, detecting means included in said first signaltranslating means effective in the absence of said interfering wave signal to derive said desired modulation components of said pulse-modulated signal and effective in the presence of said interfering signal with high intensity to derive from said received signals a heterodyne-component pulse-modulated signal having modulation components corresponding to said desired components and having a carrier frequency equal to the difference between the carrier frequencies of said received wave signals, a second signaltranslating means coupled to said detecting means and including selector circuits for translating said desired modulation components and said heterodyne-component pulse-modulated signal, rectifying means included in said second signaltranslating means eii'ective to derive said desired modulation components from said heterodynecomponent pulse-modulated signal, and means coupled to said second signal-translating means for supplying said desired modulation components to a utilizing device.

3. A receiver for deriving desired modulation components of a received pulse-modulated carrier-frequency wave signal but subject to receive concurrently therewith an interfering wave signal of different frequency than the carrier frequency of said pulse-modulated signal comprising, a first signal-translating means including selector circuits for translating both of said received signals, detecting means included in said first signaltranslating means effective in the absence of said interfering wave signal to derive said desired modulation components of said pulse-modulated signal and effective in the presence of said interfering signal with high intensity to derive from said received signals a heterodyne-component pulse-modulated signal having modulation components corresponding to said desired components, a second signal-translating means coupled to said detecting means and including selector circuits for translating said desired modulation components and said heterodyne-component pulsemodulated signal, full-wave rectifying means included in said second signal-translating means effective to derive said desired modulation components from said heterodyne-component pulsemodulated signal, and means coupled to said second signal-translating means for supplying said desired modulation components to a utilizing device.

4. A receiver for deriving desired modulation components of a received pulse-modulated carrier-frequency wave signal comprising, a first signal-translating means including selector circuits for translating said pulse-modulated signal and having a band-pass characteristic effective to translate a predetermined range of frequencies such that said receiver is subject to receive concurrently with said pulse-modulated signal interfering wave signals having carrier frequencies within a band of frequencies substantially as wide as said predetermined range, detecting means included in said first signal-translating means effective in the absence of an interfering wave signal to derive said desired modulation components of said pulse-modulated signal and eflective in the presence of an interfering signal with high intensity to derive from said received signals a heterodyne-component pulse-modulated signal having modulation components corresponding to said desired components and having a carrier frequency within a band of frequencies substantially of the width of said predetermined range, a second signal-translating means coupled to said detecting means and including selector circuits having a band-pass characteristic substantially as wide as that of said first signal-translating means for translating said desired modulation components and heterodyne -component pulse-modulated signals derived in said detecting means in the presence of said pulse-modulated signal and an interfering signal of high intensity, rectifying means included in said second signal-translating means effective to derive said desired modulation components from said heterodyne-component pulse-modulated signal, and means coupled to said second signal-translating means for supplying said desired modulation components to a utilizing device.

5. A receiver for deriving desired modulation components of a received pulse-modulated carrier-frequency wave signal but subject to receive concurrently therewith an interfering wave signal of different frequency than the carrier frequency of said pulse-modulated signal comprising, a first signal-translating means including selector circuits for translating both of said received signals, detecting means included in said first signal-translating means effective in the absence of said interfering wave signal to derive said desired modulation components of said pulse-modulated signal and effective in the presence of said interfering signal with high intensity to derive from said received signals a heterodynecomponent pulse-modulated signal having modulation components corresponding to said desired components, a second signal-translatingmeans coupled to said detecting means and including selector circuits for translating said desired modulation components and said heterodyne-component pulse-modulated signal, rectifying means included in said second signaltranslating means effective to derive said desired modulation components from said heterodyne-component pulse-modulated signal, and means coupled to said second signal-translating means for supplying substantially only said desired modulation components to a utilizing device.

I 6. A receiver for deriving desired modulation components of a received pulse-modulated carrier-frequency wave signal but subject to receive concurrently therewith an interfering wave signal of different frequency than the carrier frequency of said pulse-modulated signal comprising, a first'signal-translating means including selector circuits for translating both of said received signals, detecting means included in said first signal-translating means effective in the absence of said interfering wave signal to derive 14 said desired modulation components of said pulse-modulated signal and effective in the presence of said interfering signal with high intensity to derive from said received signals a heterodynecomponent pulse-modulated signal having modulation components corresponding to said desired components, a second signal-translating means coupled to said detecting means and including selector circuits for translating said desired modulation components and said heterodyne-component pulse-modulated signal, rectifying means included in said second signal-translating means effective to derive said desired modulation components from said heterodyne-component pulsesecond signal-translating means including a lowpass filterfor supplying substantially only said desired modulation components to a utilizing device.

'7. A receiver for deriving desided modulation components of a received pulse-modulated carrier-frequency wave signal but subject to receive concurrently therewith an interfering wave signal of different frequency than the carrier frequency of said pulse-modulated signal comprising, a first signal-translating means including selector circuits for translating both of said received signals, detecting means included in said first signal-translating means effective in the absence of said interfering wave signal to derive said desired modulation components of said pulse-modulated signal and effective in the presence of said interfering signal with high intensity to derive from said received signal a heterodynecomponent pulse-modulated signal having modulation components corresponding to said desired components, a second signal-translating means coupled to said detecting means and including selector circuits for translating said desired mod.- ulation components and said heterodyne-component pulse-modulated signal, means included in said second signal-translating means for lim-' iting the maximum amplitudes of said desired modulation components and said heterodynecomponent pulse-modulated signal to a predetermined value, rectifying means coupled to said limiting means for deriving said desired modulation components from said heterodyne-component pulse-modulated signal, and means coupied to said second signal-translating means for supplying said desired modulation components to a utilizing device.

8. A receiver for deriving desired, modulation components of a received pulse-modulated carrier-frequency wave signal but subject to receive concurrently therewith an interfering wave signal of different frequency than the carrier frequency of said pulse-modulated signal comprising, a first signal-translating means including selector circuits for translating both of said received signals, detecting means included in said first signal-translating means effective in the absence of said interfering wave signal to derive said desired modulation components of said pulse-modulated signal and effective in the presence of said interfering signal with high intensity to derive from said received signals a heterodynecomponent pulse-modulated signal having modulation components corresponding to said desired components, a second signal-translating means coupled to said detecting means and including selector circuits for translating said desired modulation components and said heterodyne-component pulse-modulated signal, means included in said second signal-translating means comprismodulated signal, and means coupled to said ing a pair of cathode-coupled electron-discharge repeater devices for limiting the maximum amplitude of said desired modulation components and said heterodyne-component pulse-modulated signal to a predetermined value, rectifying means coupled to said limiting means for deriving said desired modulation components from said heterodyne-component pulse-modulated signal, and means coupled to said second signal-translating means for supplying said desired modulation components to a utilizing device. 4

9. A receiver for deriving desired modulation components of a received pulse-modulated carrier-frequency wave signal but subject to receive concurrently therewith an interfering wave signal of different frequency than the carrier frequency of said pulse-modulated signal comprising, a first signal-translatingmeans including selector circuitsfor translating both of said received signals, detecting means included in said first signal-translating means effective in the absence of said interfering wave signal to derive said desired modulation components of said pulse-modulated signal and effective in the presence of said interfering signal with high intensity to derive from said received signals a heterodyne-ccmponent pulse-modulated signal having modulation components corresponding to said desired components, a second signal-translating means coupled to said detecting means and effectively comprising a pair of parallel-connected si nal-translating channels, one of said channels having a band-pass characteristic effective to translate substantially only saiddesired modulation components and the other of said channels having a band-pass characteristic effective to translate said heterodyne-component pulse-modulated signal, rectifying means included in said other channel effective to derive said desired modulation components from said heterodynecomponent pulse-modulated signal, and means coupled to said pair of channels for supplying said desired modulation components to a utilizing device. 10. A receiver for deriving desired modulation components of a received pulse-modulated carrier-frequency wave signal comprising, a first signal-translating means including selector circuits for translating said pulse-modulated signal and having a band-pass characteristic effective to translate a predetermined range of frequencies such that said receiver is subject to receive concurrently with said pulse-modulated si nal interfering wave signals having carrier frequencies within a band of frequencies substantially as wide as said predetermined range, detecting means included in said iirst-signal-translating means effective in the absence of an interfering wave signal to derive said desired modulation components of said pulse-modulated signal and effective in the presence of an interferin signal with high intensity to derive from said received signals a heterodyne-component .pulsemodulated signal having modulation components corresponding to said desired components and having a carrier frequency'within a band of frequencies substantially of the width of .said predetermined range, a second signal-translating means coupled to said detecting means and effectively comprising a pair of parallel-connected signal-translating channels, one of said channels having a band-pass characteristic effective to translate substantially only said desired signal components and the other of said channels hav- 16 mg a band-pass characteristic substantially of the width of that of said first signal-translating means to translate substantially only heterodynecomponent pulse-modulated signals derived in said detecting means in the presence of said pulse-modulated signal and an interfering signal of high intensity, rectifying means included in said other channel eflective to derive said desired modulation components from said heterodynecomponent pulse-modulated signal, and means coupled to said pair of channels for supplyin gal: desired modulation components to a utilizing e ce.

11. A receiver for deriving desired modulation components of a received pulse-modulated carrier-frequency wave signal but subject to receive concurrently therewith an interfering wave signal of different frequency than the carrier frequency of said pulse-modulated signal comprising, a first signal-translating means including selector circuits for translating both of said received signals, detecting means included in said first signaltranslating means efiective in the absence of said interfering wave signal to derive said desired modulation components of said pulse-modulated signal and effective in'the presence of said interfering signal with high intensity to derive from said received signals a heterodyne-component pulsemodulated signal having modulation components corresponding to said desired components, a second signal-translating means coupled to said detecting means and efl'ectively comprising a pair of parallel-connected signal-translating channels, one of said channels having a band-pass characteristic effective to translate substantially only said desired signal components and the other of said channels having a band-pass characteristic effective to translate said heterodyne-component pulse-modulated signal, rectifying means included 40 in said other channel effective to derive said desired modulation components from said heterodyne-component pulse-modulated signal, means coupled to said pair of channels for supplying said desired modulation components to a. utilizing device, and means for selectively disabling one of said pair of channels.

12. A receiver for deriving desired modulation components of a received pulse-modulated carrier-frequency wave signal but subject to receive concurrently therewith an interfering wave signal of different frequency than the carrier frequency of said pulse-modulated signal comprising, a first signal-translating means including selector circuits for translating both of said received signals, detecting means included in said first signal-translating means eflective in the absence of said interfering wave signal to derive said desired modulation components of said pulsemodulated signal and effective in the presence of said interfering signal with high intensity to derive from said received signals a heterodyne-component pulse-modulated signal having modulation components corresponding to said desired components, a second signal-translating means coupled to said detecting means and effectively comprising a pair. of parallel-connected signal-translating channels, one of said channels having a band-pass characteristic effectiv to translate substantially only said desired signal components and the other of said channels having a, band-pass characteristic eflective to translate said heterodyne-component pulse-modulated signal, rectifying means included in said other channel effective to derive said desired modulation components from said heterodyne-component pulse-modu- 17 lated signal, means coupled to said pair of channels for supplying said desired modulation components to a utilizing device, and means responsive to said interfering wave signal for disabling said one of said channels.

13. A receiver for deriving desired modulation components of a received pulse-modulated carrier-frequency wave signal but subject to receive concurrently therewith an interfering wave signal of different frequency than the carrier frequency of said pulse-modulated signal comprising, a first signal-translating means including selector circuits for translating both 'of said received signals, detecting means included in said first signaltranslating means efiective in the absence of said interfering wave signal to derive said desired modulation components of said pulse-modulated signal and effective in the presence of said interfering signal with high intensity to derive from said .received signals a heterodyne-component pulsemodulated signal having modulation components corresponding to said desired components, a second signal-translating means coupled to said detecting means and efiectively comprising a pair of parallel-connected signal-translating chan- 

